Migrating to 802.11g

by Lisa Phifer, VP, Core Competence
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New products based on the draft 802.11g standard are beginning to appear on retail shelves and prices lists. Vendors rushing to the "G party" include Actiontec (54 Mbps Wireless), Apple (AirPort Extreme), Buffalo (AirStation G54), D-Link (AirPlus Xtreme G), and Linksys (Wireless-G). Consumers struggling to choose between 802.11a and 802.11b now face another decision: whether and when to migrate to 802.11g.

Best of both worlds
The new "G" has something in common with both earlier standards:

  • Like 802.11b, G operates in the 2.4 GHz band, using the Barker Code at 1-2 Mbps and Complementary Code Keying (CCK) at 5.5-11 Mbps. These modes let G access points support older stations, easing migration from B to G.

  • Like 802.11a, G uses Orthogonal Frequency Division Multiplexing (ODFM) to increase speed. Mandatory rates are 6-24 Mbps, with optional rates up to 54 Mbps. G access points can therefore provide more bandwidth to new stations.

  • Like both predecessors, speed declines with distance, and actual throughput is about half of the link speed. But since A operates at a higher frequency, it is more easily absorbed. G should therefore be faster than A on distant stations.

    G and B similarities are no accident: 802.11g was proposed to facilitate migration to the faster, more resilient OFDM. Because vendors disagreed about how to accomplish this, the draft G standard also includes two optional modes:

  • Packet Binary Convolutional Coding (PBCC), an option in both B and G

  • A hybrid mode that combines B's CCK with G's OFDM

    This compromise was approved last September, but the standard will not be ratified until May 2003. The Wi-Fi Alliance has already conducted private interoperability tests, but formal certification will not start until the standard is ratified.

    When to migrate
    G products sold today are likely to require firmware upgrades to comply with the ratified standard and resolve early interoperability glitches when operating at higher data rates. If you can't wait three to six months to dive into G, plan ahead for upgrades.

    G throughput declines in a mixed-mode WLAN of B and G stations. Users moving from B to G may not notice, but don't expect new G stations to operate at peak efficiency until migration is completed.

    At least initially, G products will be more expensive than B products. It may be prudent to limit initial G adoption to power users and bandwidth-intensive applications.

    Enterprise gear is moving more slowly towards G. Proxim announced its first G products in February and Cisco does not plan to release G products until the standard is ratified. Organizations with existing WLANs may want to follow their vendor's migration timetable.

    Even after G matures, there will be cases where A is preferable. For example, WLANs that suffer interference in the crowded 2.4 GHz band may benefit from moving to the 5 GHz band occupied by A. High density hot spots can achieve greater aggregate capacity with A due to the number of overlapping channels in the 5 GHz band.

    In the long run, dual-band products are expected to be popular because they offer more flexibility. A+B products work in G networks – at B data rates. G products work in B networks, but not in A networks. Therefore, consumers that require dual-band flexibility may want to stick with A+B until A+G cards become available.

    Do you have comments about this article, or suggestions for Lisa to write about in future columns? Let us know!

    This was first published in February 2003

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